Patch origin: upstream
Patch status: will be part of next version

https://git.gnome.org/browse/libxml2/commit/?id=ef709ce2f7b792d5fb69ed142796d743fb1eb388

From ef709ce2f7b792d5fb69ed142796d743fb1eb388 Mon Sep 17 00:00:00 2001
From: Daniel Veillard <[email protected]>
Date: Thu, 10 Sep 2015 19:41:41 +0800
Subject: Fix the spurious ID already defined error

For https://bugzilla.gnome.org/show_bug.cgi?id=737840
the fix for 724903 introduced a regression on external entities carrying
IDs, revert that patch in part and add a specific test to avoid readding it
---
 result/valid/737840.xml         | 10 ++++++++++
 result/valid/737840.xml.err     |  0
 result/valid/737840.xml.err.rdr |  0
 test/valid/737840.xml           | 10 ++++++++++
 test/valid/dtds/737840.ent      |  1 +
 valid.c                         |  6 ++++--
 6 files changed, 25 insertions(+), 2 deletions(-)
 create mode 100644 result/valid/737840.xml
 create mode 100644 result/valid/737840.xml.err
 create mode 100644 result/valid/737840.xml.err.rdr
 create mode 100644 test/valid/737840.xml
 create mode 100644 test/valid/dtds/737840.ent

diff --git a/result/valid/737840.xml b/result/valid/737840.xml
new file mode 100644
index 0000000..433c6d6
--- /dev/null
+++ b/result/valid/737840.xml
@@ -0,0 +1,10 @@
+<?xml version="1.0"?>
+<!DOCTYPE root [
+<!ELEMENT root (elem)>
+<!ELEMENT elem (#PCDATA)>
+<!ATTLIST elem id ID #IMPLIED>
+<!ENTITY target SYSTEM "dtds/737840.ent">
+]>
+<root>
+  &target;
+</root>
diff --git a/result/valid/737840.xml.err b/result/valid/737840.xml.err
new file mode 100644
index 0000000..e69de29
diff --git a/result/valid/737840.xml.err.rdr b/result/valid/737840.xml.err.rdr
new file mode 100644
index 0000000..e69de29
diff --git a/test/valid/737840.xml b/test/valid/737840.xml
new file mode 100644
index 0000000..2d27b73
--- /dev/null
+++ b/test/valid/737840.xml
@@ -0,0 +1,10 @@
+<!DOCTYPE root [
+<!ELEMENT root (elem)>
+<!ELEMENT elem (#PCDATA)>
+<!ATTLIST elem id ID #IMPLIED>
+<!ENTITY target SYSTEM "dtds/737840.ent">
+]>
+
+<root>
+  &target;
+</root>
diff --git a/test/valid/dtds/737840.ent b/test/valid/dtds/737840.ent
new file mode 100644
index 0000000..e972132
--- /dev/null
+++ b/test/valid/dtds/737840.ent
@@ -0,0 +1 @@
+<elem id="id0"/>
\ No newline at end of file
diff --git a/valid.c b/valid.c
index 409aa81..45a3f70 100644
--- a/valid.c
+++ b/valid.c
@@ -2634,8 +2634,10 @@ xmlAddID(xmlValidCtxtPtr ctxt, xmlDocPtr doc, const xmlChar *value,
 	/*
 	 * The id is already defined in this DTD.
 	 */
-	xmlErrValidNode(ctxt, attr->parent, XML_DTD_ID_REDEFINED,
-			"ID %s already defined\n", value, NULL, NULL);
+	if (ctxt != NULL) {
+	    xmlErrValidNode(ctxt, attr->parent, XML_DTD_ID_REDEFINED,
+			    "ID %s already defined\n", value, NULL, NULL);
+	}
 #endif /* LIBXML_VALID_ENABLED */
 	xmlFreeID(ret);
 	return(NULL);
-- 
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